Laser-guided ring airfoil projectile

ABSTRACT

A system to control and correct the flight characteristics of a ring airfoil projectile while in flight. A pulsed laser system located at the projectile launch site transmits a light beam along the desired projectile flight path. A receiving system aboard the projectile detects the light beam and sends signals to control elements to maintain the projectile on the flight path. The laser beam can also be used to send arming and/or detonation signals to the projectile warhead.

United States Patent [191 McKown et al.

[ 1 Oct. 14, 1975 LASER-GUIDED RING AIRFOIL PROJECTILE [75] Inventors: Gary L. McKown, Bel Air; Leonard R. Ambrosini, Churchville, both of [73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

[22] Filed: Nov. 27, 1973 [21] Appl. No.: 419,322

[52] US. Cl. 244/3.13 [51] Int. Cl. F41G 7/00; F42B 15/00 [58] Field of Search 244/3.l3, 3.1

[56] References Cited I UNITED STATES PATENTS 3,398,918 8/1968 Girault 244/3.l3

3,614,025 l0/l97l Maillet 244/3.l3 3,746,280 7/l973 Coxe et al 244/3.l3 3,782,667 1/1974 Miller, Jr. et al. 244/3.l3

Primary Examiner-Samuel Feinberg Assistant ExaminerC. T. Jordan Attorney, Agent, br Firm-Nathan Edelberg; Robert P. Gibson; VincentW. Cleary [57] ABSTRACT A system to control and correct the flight characteristics of a ring'airfoil projectile while in flight. A pulsed laser system located at the projectile launch site transmits a light beam along the desired projectile flight path. A receiving system aboard the projectile detects the light beam and sends signals to control elements to maintain the projectile on the flight path. The laser beam can also be used to send arming and/or detonation signals to the projectile warhead.

9 Claims, 5 Drawing Figures U.S. Patent Oct. 14,1975 Sheet 1 of2 3,912,197

CONTROL DEVICE SWITCH SAFE ARM I T DETONATOR CONTROL TIME DELAY PULSE WIDTH DETECTOR DETONATING CIRCUIT HIGH PASS FILTER FM DETECTOR SENSOR U.S. Patent Oct. 14, 1975 Sheet 2 of2 3,912,197

FIG 34.

nnnnnnnnnnn LASER-GUIDED RING AIRFOIL PROJECT ILE BACKGROUND OF THE INVENTION The present invention relates generally to the field of projectile guidance and more particularly to optical guidance and control of in-flight projectiles.

Those working in the field of projectile research and development are continually engaged in the effort to improve the accuracy and dependability of warhead delivery-systems, as well as to increase the range. This effort has led to the development of laser guidance systems for rockets and projectiles However, these systems suffer from the disadvantages of complex electronics, which result in payload reduction, reliability problems, and high cost, and difficulty of control due to the parabolic flight paths of the projectiles and rockets.

The effort to improve projectile performance also led to the development of the ring airfoil projectile (RAP). The RAP is configured to exhibit aerodynamic lift and thus possesses the capability of longer range with flatter trajectory than conventional projectiles. The RAP is spun about the flight path axis at a high rate in order to gyroscopically stabilize the projectile and minimize delivery errors. While the RAP is a significant improvement over prior projectiles, it does not completely solve the above-cited problems. Incongruities in the aerodynamic parameters due to crosswinds, slight structural deformities, and launch distrubances can result in flight instability and lead to gross dispersions in delivery. In addition, an acceptable onboard fuzing system for a RAP is difficult to fabricate and has not proven feasible to date.

The present invention alleviates the above-noted problems by means of a laser guidance and control system for a RAP which does not require complex electronics or optics for its implementation.

SUMMARY OF THE INVENTION The present invention provides for the in-flight guidance of a RAP and remote control of the projectile arming and fuzing system. A pulsed laser transmitter, aligned with the projectile launch tube, sends a laser beam along the desired projectile flight path. A sensor located on-board the projectile detects the laser beam and generates signals representative of the position of the projectile relative to the laser beam. These signals are used to operate control devices to correct the flight path and keep the projectile aligned with the laser beam.

The laser beam has a controlled divergence so that at a predetermined range the beam cross section becomes equal to or largerthan the RAP diameter. At this time, the flight path control system is rendered inoperative and the warheaddetonator is armed. The laser beam can be modulated with range information so that the warhead will detonate at a desired range.

The present invention provides a simple and dependable means for controlling the dispersion and delivery of a RAP projectile and for arming and/or detonating the warhead at a controllable range. As will be futher described below, the sensor and associated signal processing electronics, and the control devices, are not complex or bulky; thus, payloads are maximized, power creased since the projectilecan be armed by remote control after a considerable downrange traverse.

Therefore, it is an object of the present invention to provide a system for guiding a'RAP while in flight.

Another object of the invention is to provide a laser guidance system for a RAP.

A further object of the invention is to provide a laser guidance and control system, for controlling the dispersion of a RAP and arming its warhead after launch.

Still another object of the invention is to provide a laser control system which can detonate the warhead in a RAP by remote control.

These and other objects and advantages of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the relationship of the laser beam to the in-flight RAP. 1

FIG. 2 shows, in block diagram form, the control and detonating circuits.

FIG. 3A and 3B illustrate the operation of the device when functioning to control the RAP flight path.

FIG. 4 illustrates the relationship between the receipt of pulses by the sensor and the actuation of the controls.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the numeral 12 represents a cross section of the RAP. The RAP is shown here inflight immediately after launch. The projectile is launched by rifled gun tube 16 with a velocity and spin rate commensurate with the range capability desired. A pulsed laser system 18, which may be of the injection diode, solid state, or any other type, is disposed centrally within the projectile launch tube. An adjustable lens system 20 of conventional design collimates the laser output into a beam 22 with small divergence. Beam width and divergence settings will depend on the size and function of the particular system employed as well as the desired range of flight path control and armmg.

The RAP has one or'more photosensors 24 mounted on the tail portion thereof adjacent optical filter 52. A control device 26 is also mounted on the RAP. As illustrated in FIG. 1, the diameter of the laser beam 22 immediately after launch is less than the diameter of RAP 12 and, thus, the beam does not illuminate sensor 24.

FIG. 2, which illustrates the signal processing circuitry mounted aboard the RAP, can be conveniently divided into two portions, control circuit 50 and detonating circuit 60. The control circuit includes sensor 24 which is located externally as shown in FIG. 1. The sensor must sense only radiation of the same frequency as the laser beam. Either sensor 24 can be of the type sensitive to only a narrow spectrum of radiation or an optical filter 52 can be placed between the laser source and the sensor to pass only the laser beam frequency. When the pulsed laser beam impinges on sensor 24, it puts out a signal to amplifier 53. The operation of control cir cuit 50 can be best understood by referring to FIGS. 3A and 3B. FIG. 3A illustrates the situation where the spinning projectile 12 has begun to wander off the desired flight path. As shown in FIG. 1, when the projectile is on the flight path the laser beam 22 does not illuminate the photosensor 24. In FIG. 3A, the laser beam 22, shown in cross section, illuminates the sensor 24 for part of the spin cycle. Assuming that the projectile is spinning clockwise, the sensor 24 will be illuminated from point X to point Y. The sensor will produce an electronic pulse train with a period corresponding to the spin rate of the projectile, such as is shown in FIG. 3B, graph A, and these pulses will be amplified by amplifier 53. The amplified pulses are fed to detector 54 which produces a single pulse as shown in FIG. 3B, graph B. The pulse is fed to time delay circuit 55 which delays the pulse a period of time proportional to the projectile spin rate. The function of time delay circuit 55 will be further described below. The delayed pulse, shown in FIG. 3B, graph C, is fed through normally closed switch 56 to normally open switch 57. The pulse causes switch S7 to close momentarily and activate control device 26 for a predetermined period of time. The control device may utilize any or all of the following methods for correction of the flight path:

1. release of gas from ports, possibly via a fluidic amplifier; V V

2. movement of center-of-gravity with respect to center-of-pressure of the lifting surface;

3. change in airfoil lifting surfaces;

4. projection of drag surfaces. These methods are merely exemplary and any suitable control method can be used. The controlling torque thus applied will act on the gyroscopic system to cause precessional motion about a perpendicular axis. Appropriate control action is assured by the time delay of the control signal to yield a 90 phase angle between sensing and control action, taking into account the inherent mechanical delay.

The time sequence of events in the control cycle are illustrated in FIG. 4, in which projectile 12 is shown spinning clockwise. The presence of the beam 22 is sensed at point A and the electronic signal is processed and delayed by control circuit 50 during the time interval A-B, or n/RPM l-AB, depending on the mechanical time constant in the control action. If a positiveacting control device is employed, control action occurs during the time interval B-C, and the interval C-D is used for reset of the electronics. If a negative-acting control device is employed, further time delay in the interval B-B is utilized with control action occurring during interval BCand electronic reset occurring during interval CD. This sequence of events is repeated at the projectile spin rate until the sensor is no longer in contact with the beam. Very small control increments can thus be employed in order to minimize erratic behavior caused by the application of gross corrective action.

Returning now to FIG. 2, the detonating circuit 60 will be discussed. Circuit 60 performs two functions; first, it arms the warhead and deactivates the control devices; and secondly, it fires the detonator at a controllable time.

As previously mentioned, the laser beam 22 has a certain degree of divergence which can be controlled by lens system 20. Warhead arming is effected by electronically sampling the modulation width of the sensor output. When the laser beam 22 cross section becomes comparable to or larger than the RAP diameter, the sensor output modulation approaches zero frequency. That is, the width of the pulse out of detector 54 approaches infinity. This condition is detected by a pulse width detector circuit 61 which outputs a signal to switch 56 to irreversibly deactivate the control system in order to cut off guidance operation far downrange and thus to prevent the detonating scheme from initiat- 5 ing control action. The signal from pulse width detector 6l also energizes safe/arm circuit 62 to arm detonator 63. The pulse width detector may be of the high-pass filter type with cut-offclose to DC.

Detonation is actuated by transmitting a coded signal obtained by frequency modulating the laser beam pulse rate in consonance with set range or with the output of a laser range-finder. The coded signal is passed by highpass filter 64 to PM detector and discriminator 65 which compares the signal to a built-in preset gating code 66. When the proper coded signal is detected, the detonator is energized. 7

Obviously, utilization of detonating circuit 60 requires correlation of laser beam divergence with munition characteristics and/or range desired. This is accomplished by simple linear manipulation of the collimating lens system 20, calibrated for various ranges. Such focusing action may occur automatically by using a rangefinder output to control the lens position.

There has been disclosed herein a system whereby a RAP can be laser-guided downrange to the point where the beam divergence becomes equal to the projectile diameter, whereupon the detonator is armed, the control system deenergized, and the projectile commences to free-fly onto the target and/or detonates at a specified range. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

I. In a system for guiding, along a predetermined path, a projectile of the type which spins about its flight axis comprising:

means for launching the projectile along said path;

means for emitting a beam of pulsed monochromatic light along said predetermined path so as to impinge on the projectile;

means mounted on the exterior of the projectile for generating a signal when illuminated by said light beam; and,

means disposed within the projectile for controlling the direction of flight of the projectile in response to said signal, the improvement wherein:

said generating means comprises at least one photosensor disposed on the projectile a predetermined distance from said flight axis, whereby said spinning photosensor describes a circle of predetermined area; and said light beam emitting means comprises a laser system disposed at the launch site including means for varying the cross-sectional area and the divergence of the beam in such a manner that the cross-sectional area of the beam is smaller than the area of said circle at the launch site and is equal to the area of said circle at a predetermined distance from the launch site.

2. The system of claim 1 wherein said direction controlling means comprises:

one or more control devices on the exterior surface of the projectile;

means for receiving the signal from said photosensor and generating a pulse in response thereto; and,

switch means for activating said control devices in response to said pulse.

3. The system of claim 2 wherein said direction controlling means includes a time delay circuit connected between said pulse generating means and said switch means to delay the activation of said control devices until they are properly oriented. I

4. The system of claim 3 wherein the amount of time delay is related to the projectile spin rate in such a manner as to provide a 90 phase angle between sensing and control action.

5. The system of claim 3 further including:

a warhead carried by said projectile; and,

means for arming and detonating said warhead when the projectile has traveled said predetermined distance.

6. The system of claim 5 wherein said arming and detonating means comprises:

a pulse width detector connected to receive said pulse; and,

a safe and arming circuit connected to the pulse width detector and responsive thereto to arm said warhead.

7. The system of claim 6 wherein:

said laser system includes means for modulating the pulse repetition frequency of the laser beam as a function of projectile position; and,

said arming and detonating means includes means for demodulating the laser beam and detonating the warhead at a predetermined position.

8. The system of claim 7 including means for permanently deactivating said direction controlling means when the warhead is armed.

9. The system of claim 8 wherein the projectile is a ring airfoil projectile. 

1. In a system for guiding, along a predetermined path, a projectile of the type which spins about its flight axis comprising: means for launching the projectile along said path; means for emitting a beam of pulsed monochromatic light along said predetermined path so as to impinge on the projectile; means mounted on the exterior of the projectile for generating a signal when illuminated by said light beam; and, means disposed within the projectile for controlling the direction of flight of the projectile in response to said signal, the improvement wherein: said generating means comprises at least one photosensor disposed on the projectile a predetermined distance from said flight axis, whereby said spinning photosensor describes a circle of predetermined area; and said light beam emitting means comprises a laser system disposed at the launch site including means for varying the cross-sectional area and the divergence of the beam in such a manner that the crosssectional area of the beam is smaller than the area of said circle at the launch site and is equal to the area of said circle at a predetermined distance from the launch site.
 2. The system of claim 1 wherein said direction controlling means comprises: one or more control devices on the exterior surface of the projectile; means for receiving the signal from said photosensor and generating a pulse in response thereto; and, switch means for activating said control devices in response to said pulse.
 3. The system of claim 2 wherein said direction controlling means includes a time delay circuit connected between said pulse generating means and said switch means to delay the activation of said control devices until they are properly oriented.
 4. The system of claim 3 wherein the amount of time delay is related to the projectile spin rate in such a manner as to provide a 90* phase angle between sensing and control action.
 5. The system of claim 3 further including: a warhead carried by said projectile; and, means for arming and detonating said warhead when the projectile has traveled said predetermined distance.
 6. The system of claim 5 wherein said arming and detonating means comprises: a pulse width detector connected to receive said pulse; and, a safe and arming circuit connected to the pulse width detector and responsive thereto to arm said warhead.
 7. The system of claim 6 wherein: said laser system includes means for modulating the pulse repetition frequency of the laser beam as a function of projectile position; and, said arming and detonating means includes means for demodulating the laser beam and detonating the warhead at a predetermined position.
 8. The system of claim 7 including means for permanently deactivating said direction controlling means when the warhead is armed.
 9. The system of claim 8 wherein the projectile is a ring airfoil projectile. > 